Not Applicable
Resistance butt welding and resistance butt flash welding machines are well known in the art. In a resistance butt welding process, two pieces of material, held by clamps, also called platens, are brought into contact with each other. Once the ends are in contact, an electric current is passed through the pieces. The high resistance at the interface between the two pieces causes heat to be generated. The current is passed through until the pieces are hot enough to be forged through a process called upsetting. Once the ends come into contact a constant pressure is applied during the heating process. Motion starts to occur as soon as the metal becomes forgeable.
The process of resistance butt flash welding starts by bringing the ends of the clamped pieces to be welded into contact with each other. A voltage is placed across the pieces as they approach each other. As the pieces touch, the metal heats and is expelled from the contact area. The expulsion, called flashing, is continued at a very precise rate. After flashing for a specified time and distance, a high-force, high-speed move, known as upset, is completed. The optimum amount of force and distance to be moved vary with the nature, thickness and mass of the pieces to be welded. The flashing motion has traditionally been made using a cam, cam follower, and the necessary linkage to attach the cam follower to the movable platens. See for example, U.S. Pat. No. 3,694,613. This method works well for a single flashing (cam) profile. However, when the material to be welded requires different flashing (cam) profiles to weld the work pieces together consistently, changing the flashing (cam) profiles or making an adjustment contained within the cam follower linkage is difficult and time consuming. Other factors in controlling the welding are the timing of changes in the motion, control of speed of the motion, and control of the upsetting force required to forge the work pieces together. The timing changes are generally done with cam switches, which are linked to the flashing cam. These cam switches are difficult to set up accurately and therefore limit the precision of the timing for motion changes.
For a discussion of the two techniques, see Derby et al, U.S. Pat. No. 6,169,263.
The servo system of this invention will work with both processes, but provides more benefit as applied to the resistance butt flash welding process, because of the easy replication of the cam./cam follower motion.
More recently, the energizing force for the welders has been a hydraulic cylinder. The amount of force and speed of movement of the work pieces toward one another has been controlled by the admission to and release from the cylinder of hydraulic fluid, or air, if a pneumatic system is employed. See, for example, U.S. Pat. No. 6,169,263, Derby, Jr. et al, and U.S. Pat. No. 4,940,876, Kuchuk-Yatsenko et al. The hydraulic system is generally more expensive and less accurate than the cam system and than the system of the present invention.
In accordance with this invention, generally stated, in a butt welding system, the timing of changes in the motion, control of speed of the motion, and control of the upsetting force required to forge the work pieces together are controlled and actuated by a computer-controlled or other programmable electronic device-controlled linear motor or, preferably, by a similarly controlled rotary motor servo ballscrew drive. The resultant welds can be tempered at the loading station, or moved to a reheat station apart from the loading station at which the weld is made. The pressure applied to the work pieces during the upsetting process can be controlled by establishing and monitoring current limits for the motor being used, for example, or determining and monitoring the distance to be traversed by one work piece as it approaches the other. The speed of advancing of one of the work pieces with respect to the other can be controlled by establishing a torque-speed chart, moving the pieces to a specific relative position to begin with, and monitoring current draw as the pieces meet. The optimum conditions can easily be established experimentally for any specific machine and particular application. Suitable servo systems are available from Pacific Scientific, Allen Bradley, Siemens or GE Fanuc, ball screw servo systems being commonly used with CNC equipment on machine tools.